Vacuum pump system

ABSTRACT

A vacuum pump system comprising a plurality of vacuum pumps which are connected to one another in parallel and are each connected on an inlet side to a chamber, having an outlet line which is connected on the outlet side of the vacuum pumps, and an intermediate line which connects the inlet side of at least one vacuum pump to the outlet line, wherein all the vacuum pumps are connected in parallel during a pumping-out period and at least one of the vacuum pumps is connected in parallel with the other vacuum pumps as a backing pump during an idle period.

BACKGROUND 1. Field of the Disclosure

The present disclosure relates to a vacuum pump system for evacuating a chamber, in particular a process or lock chamber.

2. Discussion of the Background Art

Vacuum pump systems for regularly evacuating large chambers are known from prior art, FIG. 1. Frequently, vacuum pumps operating in a dryly compressing manner are used for this purpose. As a rule, these are combinations of backing pumps, such as screw pumps, claw pumps or multi-stage Roots pumps, and parallel-connected Roots pumps. In large pump systems a plurality of pumps and a plurality of Roots pumps are connected in parallel.

Typically such pump systems are used in lock chambers, for example loadlock or unloadlock, e. g. in coating plants. In these plants a chamber must be pumped down from atmospheric pressure to a transfer pressure of typically approximately 0.1 mbar to 10 mbar within a short period of time, e. g. a pumping-down period of 20 seconds to 120 seconds. Subsequently, a vacuum pump is separated from the chamber to be evacuated by a valve on the inlet side and operates for a certain period of time, typically one to ten times the pumping-out time, in discharge pressure operation.

Further typical applications are large process chambers for heat treatment or refinement of metals. In this case typical pumping-out periods are 2 to 30 minutes. Thereafter a low gas flow must continue to be pumped out, which is however considerably smaller than the gas flow necessary for realizing the pumping-out period. A typical hold period for this operating pressure amounts to two to ten times the pumping out period.

In such applications the vacuum pump system must be very largely dimensioned for realizing the short pumping-out period. During an idle period and/or during a hold period large suction capacities of the pump systems are however not necessary. Consequently, during an idle and/or during a hold period an unnecessarily high energy expenditure of the pump is required.

For reducing a high power consumption of pump systems during the idle and/or hold period different approaches are known.

Some pump systems having backing and/or Roots pumps are temporarily shut down. In this case it is disadvantageous that the pumps become cold which has a negative effect on the service life of the components. Further, linings may stick together and block the rotors. During short idle and/or hold periods the pumps must frequently be accelerated again which requires more power and very largely dimensioned motors. It is therefore not common practice to shut down pumps.

Further it is known from prior art that on the outlet side of each backing pump an additional small auxiliary pump is connected in series, FIG. 3. This may e. g. be an ejector pump or another smaller backing pump. Parallel to the auxiliary pump a switch valve or a check valve having an adequate cross section must normally be arranged in order to avoid too high pressures between the backing and auxiliary pumps during the pumping-out period. These solutions are disadvantageous because of the large number of additional pumps. Moreover, very small auxiliary pumps, such as ejector pumps, for example, cannot reduce the outlet pressure of the backing pump rapidly enough for attaining adequate power savings during short idle and/or hold periods. Further, the auxiliary pumps require energy for operation.

Another solution which is known from prior art is that on the outlet side of the backing pump a small number of further large backing pumps may be arranged as large auxiliary pumps, FIG. 2. They are connected in series with the backing pumps via a pipeline system. In this case, too, at least one valve having an adequate cross section must normally be arranged parallel to the auxiliary pump for avoiding high pressures between the backing and auxiliary pumps during the pumping-out period. This solution is disadvantageous due to the additional purchase and operating costs as well as the space required for the auxiliary pumps.

It is an object of the present disclosure to provide an improved pump system which consumes less power, in particular during the idle and hold periods.

SUMMARY

This object is achieved with a pump system having a plurality of vacuum pumps which are connected in parallel with each other and are each connected to a chamber at their inlet side, FIG. 4. The pump system further comprises an outlet line which is connected to the outlet side of the vacuum pumps. In addition, the pump system comprises an intermediate line which connects the inlet side of at least one of the vacuum pumps with the outlet side. During a pumping-out period all vacuum pumps are connected in parallel and during an idle and/or hold period at least one of the vacuum pumps is connected in series with the other vacuum pumps as a backing pump.

Due to the parallel connection of all vacuum pumps of a pump system during the pumping-out period the full suction capacity is available for the pumping-out process. The vacuum pump system further comprises switchover means both in connections of the inlet sides to the chambers and in an intermediate line. These switchover means may comprise valves, for example. During an idle and/or hold period thus one of the vacuum pumps can be connected in series with the other vacuum pumps as a backing pump. This is realized by a corresponding arrangement of the switchover means such that they block or release the connection in such a way that the vacuum pumps are connected in series or in parallel to each other in a different manner. Thereby the outlet pressure of the vacuum pumps is rapidly decreased and the power consumption is considerably reduced. However, the pumps continue to operate such that they can be used for the next pumping-out cycle without any loss of time.

Shutting down of certain pumps is thus not necessary such that the pumps remain warm and continue to be fully operable. Another advantage results from the drives not having to be designed for frequent accelerations and no additional pumps being required. An additional expenditure for the pump system according to the disclosure is merely limited to relatively small dimensioned pipelines and switchover means, for example valves, as well as modifications to a pump control unit.

Due to the reduced energy expenditure of the pump system the pumps are operated in a relatively cold state such that the service life of normal wear parts is significantly increased, for example oil, bearings, seals, power electronics in the drive unit. Further, due to this reduced energy expenditure attributable to reduced waste heat the costs for air-conditioning of the installation site and cooling of the pumps are reduced. Due to the reduced pressure in the outlet during operation condensation of vapors in the pumps is also avoided, whereby damage caused by corrosion can be reduced.

In the case where at least one vacuum pump can be connected in series as a backing pump a very low discharge and/or operating pressure can be attained.

Thus particular process steps can be made possible without any additional pumps. For example, leak detection in the plant prior to the actual process operation is thus possible since a leak detection normally requires a low operating pressure. During an idle and/or hold period realized according to the disclosure, the sound level of a pump system decreases since most of the pumps have a lower noise emission at a reduced load.

The pump system according to the disclosure allows for a high redundancy since even if individual pumps in such a group fail the process is allowed to be continued. Thus all pumps can fulfill their tasks even without any auxiliary pumps. In addition, a plurality of pumps may be incorporated in such a way that they can be used as an auxiliary pump. Besides a reduction of the power consumption and thus reduced operating costs, the CO₂ footprint for such an application according to the disclosure is improved.

For the operation according to the disclosure it is particularly preferred that the vacuum pumps which are to be connected in series as backing pumps meet certain technical requirements. It is particularly preferred that these vacuum pumps are sealed such that they can reliably operate at strongly reduced outlet pressures without any gas or oil leakage. Particularly preferred are outlet pressures of the backing pumps during idle and/or hold operation in a range of 10 mbar to 500 mbar. Further, it is particularly preferred that the thermal behavior of the pumps reliably allows for operation at a strongly reduced outlet pressure. This aspect relates in particular to the gap heights, the oil viscosity and the lubrication of bearings.

In addition, it is particularly preferred that oil-lubricated spaces are sealed towards a working space such that even at very rapid cycles no strong oil spreading takes place. In addition, shaft seals are preferably to be configured such that they do not prematurely suffer from wear caused by rapidly changing pressure differences. One possibility in this respect is the use of compensation lines between oil-lubricated spaces and the working space which comprise an oil separator.

Further advantageous configurations and modifications are shown in the following figures. However, the respective resultant features are not limited to the individual figures or configurations. Rather, one or more features of the above description can be combined with individual or a plurality of features of the figures for providing further modifications.

BRIEF DESCRIPTION OF THE DRAWINGS

In the figures:

FIGS. 1 to 3 show embodiments according to examples of prior art, and

FIGS. 4 to 6 show exemplary embodiments according to the disclosure.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 shows a vacuum pump system 1 having a lock chamber 10 and parallel-connected pumps P1-P5 each of which is connected on its inlet side with the lock chamber. In addition, the vacuum pump system 1 comprises valves V1-V5, by means of which the connection from the pump inlets of the pumps P1-P5 to the lock chamber 10 can be disconnected. The illustrated vacuum pump system is known from prior art. During a pumping-out period the valves V1-V5 are open. The pumps P1-P5 consume a lot of power during the pumping-out period and operate at full speed. The pressure in the lock chamber decreases continuously.

During an idle period the valves V1-V5 are dosed and the pumps P1-P5 operate at full speed, wherein the power consumption essentially corresponds to that of the operation at a discharge pressure and continues to be relatively high. The pressure in the lock chamber is equal to a transfer pressure.

During a hold period the valves V1-V5 are open and the pumps P1-P5 operate at a low operating pressure.

The vacuum pump system illustrated in FIG. 2 is known from prior art. The pump system is extended by a relatively largely dimensioned auxiliary pump P26 as well as by the check valves CV1-CV5.

The parallel-connected pumps P21-P25 are connected with a chamber 20. During a pumping-out period both the valves V21-V25 and the check valves CV21-CV25 are open. The inlet pressure of the additional auxiliary pump P26 is approximately equal to the outlet pressure of the auxiliary pump.

During an idle period the valves V21-V25 are closed. Subsequently, the check valves CV21-CV25 are also closed. During this operation the inlet pressure of the auxiliary pump P26 is considerably lower than the outlet pressure of the auxiliary pump P26.

FIG. 3 shows a prior art configuration of a vacuum pump system for a lock chamber 30 having small auxiliary pumps P33 and P34. An ejector pump may be selected as the auxiliary pump, for example.

During a pumping out period the valves V31 and V32 as well as the check valves CV31 and CV32 are open. The inlet pressures of the auxiliary pumps P33 and P34 are approximately equal to the outlet pressures of the auxiliary pumps P33 and P34.

During an idle period of the pump system 3 the valves V31 and V32 are closed.

The check valves CV31 and CV32 are also closed during an idle period. The outlet pressures of the auxiliary pumps P33 and P34 are substantially larger than the inlet pressures of these auxiliary pumps P33 and P34 during the idle period.

FIGS. 4 to 6 show configurations of the vacuum pump system according to the disclosure.

The vacuum pump system shown in FIG. 4 comprises five parallel-connected vacuum pumps P41, P42, P43, P44, P45. The inlets of the vacuum pumps P41, P42, P43, P44, P45 are connected with a vacuum chamber 40. Between the respective vacuum pumps P41, P42, P43, P44, P45 a valve V41, V42, V43, V44, V45 is provided. The outlet sides of the pumps P41, P42, P43, P44, P45 are connected with a common outlet 41 via check valves CV41 CV42, CV43 CV44, CV45.

In a connecting line 42 in which a valve V46 is arranged the pump P41 can be connected in series with the pumps P42, P43, P44, P45 in the exemplary embodiment of the vacuum pump system of FIG. 4.

The vacuum pump P41 which is to be used as a backing or as an auxiliary pump can generally be smaller designed than the other vacuum pumps. Thus the power consumption during the idle and/or hold operation is further reduced. FIG. 4 shows a vacuum pump system where the valves V41-V45 are open and the valve V46 is closed during a pumping-out period. In addition, the check valves CV41-CV45 are open during the pumping-out period.

During the idle period the valves V41-V45 are closed, V46 is open. The check valve CV41 is also open during this operation as long as the pump system is evacuated by the pump P41. Thereafter it is closed. The check valves CV42-CV45 are closed during the idle operation. The reduction of the power consumption in the idle state amounts to up to 40% in some exemplary embodiments. In particular, the described series connection of the vacuum pump as a backing pump can also be used for improving the feed of light gases. In addition, this pump connection can also be used for regulating the chamber pressure or the process flow. The auxiliary pump ensures that the operating pressure range is reliably reached. The backing pumps can then be reliably regulated in a very large speed range.

FIG. 5 illustrates a minimal configuration for lock chambers in the exemplary embodiment of FIG. 5 a pump system merely having two vacuum pumps P51, P52 is selected as an example. They comprise a common inlet line which is connected with a vacuum chamber 50 via a valve V52. Merely the outlet of the vacuum pump P52 is connected with the common outlet 51 via a check valve CV51. The outlet of the pump P51 is directly connected with the common outlet 51. Via an additional line 52 in which a valve V51 is arranged and which extends from the outlet of the pump P52 to the inlet of the pump P51 the pump P51 can evacuate the other pump P52 from both sides during the idle period. In the example of FIG. 5 the pumps P51 and P52 can however not be connected in series.

Similar to FIG. 5, FIG. 6 shows a minimal configuration for process chambers. During the hold period V61 is open such that P62 and P61 are evacuated from both sides. During the pumping-out period V6 is closed such that the process chamber can be evacuated within a short period of time. In both configurations of the vacuum pump systems 5 and 6 further pumps can be connected in parallel with the pumps P52 and P62 and operated accordingly.

The solutions described here can be realized for combinations with two or more backing pumps. The respective number and size of the pumps can be freely adapted to the application. The Roots pumps connected in series with the backing pumps have generally no influence on the solutions. Therefore they have net been illustrated in the examples. 

What is claimed is:
 1. A vacuum pump system having a plurality of vacuum pumps which are connected in parallel with each other and are each connected on an inlet side with a chamber, having an outlet line which is connected with the outlet side of said vacuum pumps, and an intermediate line connecting the inlet side of at least one vacuum pump with said outlet line, wherein during a pumping-out period all vacuum pumps are connected in parallel, and during an idle period the inlet side of at least one of said vacuum pumps is connected with the outlet side of the remaining vacuum pumps as a backing pump.
 2. The vacuum pump system according to claim 1, wherein during the idle period the vacuum pump whose inlet side is connected with the outlet side of the remaining vacuum pumps is connected in series with the other vacuum pumps.
 3. The vacuum pump system according to claim 1, wherein the outlet side of the vacuum pump is connected with the outlet line via a check valve.
 4. The vacuum pump system according to claim 1, wherein in front of each of the vacuum pumps a valve is arranged, as well as in particular another valve is arranged in the intermediate line for controlling a parallel or series connection of the individual vacuum pumps with each other.
 5. The vacuum pump system according to claim 1, wherein the at least one of the vacuum pumps whose inlet side is connected with the outlet side of the remaining vacuum pumps in the idle state and which is in particular connected in series with the other vacuum pumps is smaller dimensioned than the other vacuum pumps. 